Despite having the highest levels of healthcare spending in the world, the U.S. ranks last in key areas including the efficiency and quality of care delivered. The Institute of Medicine estimates that $765 billion dollars are wasted every year due to systemic flaws in care delivery designs and treatment patterns, and urges rapid system learning to improve performance. Success in reducing cost or increasing efficiency, however, must not be achieved at the expense of the quality of care delivered to patients. Lean management is an industry- based intervention that has been successful in maximizing efficiencies, minimizing costs, and improving the quality of products and services delivered to consumers. Lean is rapidly becoming one of the leading methods used in both public and private healthcare systems to improve short-term efficiency and quality, while serving as a foundation for longer-term system transformation. Despite the increasing adoption of Lean in health care, there are few rigorous studies of its impacts, and particularly of Lean as a basis for system-wide improvement in cost and quality measures. The goal of this study is to explore the impacts of Lean management on several important outcomes. Specifically, Aim 1 will determine the impact of Lean process improvements on technical efficiency, as measured by inputs (e.g., supplies, physician and non-physician time and staffing) relative to services provided. Aim 2 will explore Lean implications for health system affordability, as indicated by resource use per patient population, and per acute and chronic episode of care (back pain, bronchitis, diabetes, hypertension), while monitoring trends in clinical quality. Finally, Aim 3 will evaluate the impact of Lean redesigns on patient experiences with care delivery by examining changes in patient-reported satisfaction, access (e.g., to office visits, provider response time to patient messages), and patient flow (e.g., time spent in waiting/exam room). These metrics will be examined in 46 primary care departments across nearly 20 geographically distinct clinic locations of a large, healthcare delivery system serving nearly one million patients across four counties. As Lean was implemented in a systematically staged manner-first in one pilot clinic, then three beta clinics, followed by thirteen remaining clinics with staggered implementation start times-this already completed natural experiment allows a unique opportunity to leverage real-world, operational activities for rigorous, scientific study. A quasi-stepped wedge design with segmented regression will be applied to organizational metrics and physician/patient time data as documented and analyzed in novel ways using our time-stamped EHR system. Findings from this proposed study would add substantially to knowledge about Lean in health care, and may benefit scientific, practicing, and policy communities as Lean grows in popularity as a vehicle for improving value in U.S. health care.